Air in pumped system

[btibuzz]

Been browsing the forum for a couple of days and whilst I've found similar problems to mine - I don't think I've found exactly what I need - hope someone can make sense of it.

Situation is...

2nd floor flat - two bathrooms, one kitchen running off a combi boiler.
Water to the taps pumped from hot and cold tanks in the loft, via a Stuart Turner Dual Monsoon Pump (Standard - Not universal).

This was put in 4-5 yrs ago when place was converted - I specced tanks and pumps rather than relying on the combi, even though mains pressure is ok because I wanted full-on showers. (Which they are)

Had a leaking shower valve, and turned off feeds in order to fix. The only isolation valve for the hot feed was a gate valve between the tank and the pump. Once fixed, the gate valve (one with the red cage head) for the 22mm hot feed wouldn't turn back on. Don't really understand the boiler/hot-tank system so didn't want to drain system and used a wickes pipefreezing kit (I know) to allow me to swap out the valve. All was going well until I broke an elbow near the tank while tightening the new valve.

Got it under control eventually replacing the elbow and the valve but I did lose a lot of water and ever since then the hot feed has spluttered and spurted pretty much continously.

It is worse when you first open a tap, but it occurs when any or all 6 of the hot taps are opened. I assume I've got air in the hot circuit somewhere that's interfering with the pump.

When you listen to the vent pipe from the hot tank that's hanging over the cold tank you can hear a sucking noise that coincides with the spluttering supply.

From reading the forums there appears to be 2 main ways of getting rid of air in the hot circuit....

1) Connecting mains tap to hot tap and opening to force air back out the other way into the tanks.

However as the system is pumped would this even work? and secondly I don't have a mains tap. (Secondary Question - Should I have one? Kitchen cold is fed from tank like all the others.)

2) Turn off (bung) cold feed to hot tank, drain hot tank, open taps, to void system, turn on cold feed to hot tank, once water comes out of all taps, close taps. From what I understand this should allow the system to fill properly (allowing trapped air out the vent?)

My concern with this is - won't that leave the pumps pumping air until the system starts filling again? IS that ok or would I knacker the pump - Will a drained system be a problem for the combi?

Apologies for the long mail, and feel free to shout abuse if I've missed something obvious, or if you think I'm in over my head.

Cheers

Paul

 

[Alanka]

I assume the hot water cylinder is a conventional indirect one (and not a 'primatic' type - which would be totally unsuitable for this application)?

Are all the pipe runs from the cold water tank to the hot water cylinder level, or at a slight fall, so that any air expelled from the heated water can pass upwards along the pipes to the vent? If not, consider adjusting pipes to achieve this, and/or fit one or two automatic air vents at places where air may collect to form airlocks.

You should never run a shower pump without water, because the bearings usually rely on the pumped water for their lubrication, and could seize up in a very short time! (I've done it in under a minute!)

Your cold water supply at the sink should be straight from the mains, not from a tank - but if your cw tank is to regulation you probably won't be at risk from decaying mice droppings etc.!

 

[WHPES]

There are two problems with your pumped system - hot and cold are run by a twin pump. This should have been two single pumps as when hot or cold only is run, the other side of the pump is running, will build up pressure destroy the seals.

Secondly, my guess is the draw off point from the cylinder is in the wrong place and is sucking air from the vent pipe. Fit an Essex flange to the cylinder and draw off fom there - should fix your problem.

Cold water should be fed from the rising main unless you have a WRAS compliant sealed header tank or risk of disease if drunk.

 

[btibuzz]

Thanks for that guys - I'll double check some of that stuff when I get the chance....

I do know the cold tank is higher than the hot tank - never actually checked pipe levels etc , that's one of the things to look at.

The cold tank was new ~5yrs back when whole system was put in, so I assume the kit itself is compliant. It was during a fairly major extension/conversion so I do know we were subject to building control visits during the work so I would hope everything would be OK, but I don't really know what they checked as far as the plumbing goes.

The tank itself is square black plastic with a clip on lid, not sealed like tupperware but there's a definite click as it locates.

However, there's a slot cut in the lid to allow it to fit round the vent pipe from the hot tank. No idea on WRAS specs and whether it's compliant - Been bouncing round the WRAS site but it's a bit low on details for installation notes.

tbh I assume it's not. - It's definitely not what I'd call sealed.

Regarding the pump, Stuart Turner reckon it's OK for whole house vented systems - however in the small print it does state you can't use it in feeds for condenser dryers as they use constant cold flow - I assume it's a timing thing. OK for standard domestic use, but long term constant differential flow is an issue.

As soon as their pump helpline comes free I'll try to get more from them. tbh at the price of pumps I'll look at replacing when this one fails rather than changing out ahead of time.

But looks like I'm going to have to trace the mains in to get a decent feed to the kitchen cold tap.

One other thing - bear in mind the whole system worked before I had my episode with the gate vlave so it must be possible to get it working (as long as I've not changed anything with my fixes....)

Paul

 

[prs1]

1-Isolate gate valve on feed to hot water cylinder.
2-put hose on drainvalve at base of hot water cylinder and remove 5 or 6 bucketfulls of water.
3-close drainvalve.
4-open all hot taps.
6-open gate valve and allow cylinder to fill pushing air out of open taps
when taps are flowing correctly shut them on making sure that they are running correctly.
Dont try and rush it it may take a couple of goes.
make sure u take enough water out of the cylinder say 1/3rd pump off when draining and pump on to fill!
Good luck
paul

 

[WHPES]

No, it's not compliant if what you describe is the case. The vent pipe should fit in a special gromet to seal between the pipe and the tank lid. It should have a mushroom shaped breather plus various other stuff. Also (I think is so but please anyone else on the forum who may know otherwise say so) the hot and cold for a shower must be fed from the same tank or at least two tanks linked together (correctly).

When your pump fails (which it will), replace with two idependent pumps for hot and cold

Not all building inspectors know the details on the plumbing stuff.

 

[btibuzz]

1-Isolate gate valve on feed to hot water cylinder.
2-put hose on drainvalve at base of hot water cylinder and remove 5 or 6 bucketfulls of water.
3-close drainvalve.
4-open all hot taps.
6-open gate valve and allow cylinder to fill pushing air out of open taps
when taps are flowing correctly shut them on making sure that they are running correctly.
Dont try and rush it it may take a couple of goes.
make sure u take enough water out of the cylinder say 1/3rd pump off when draining and pump on to fill!
Good luck
paul

Late response bump on thread (I've been kind of busy) - Did this and it sorted the pulsing.

Thanks.

Also armed with a bit more info I looked at the whole system a bit deeper. I found that all water in rear bathroom (shower, sink and toilet) is fed from tanks via pump. However the front of the flat (kitchen and bathroom) it's only the hot that's fed from pump, all colds are direct from mains. Also there was no mains stopcock in the property, only way of stopping the cold feed was at the meter in the street. Fortunately that's all pretty new with a plastic tap that worked freely.

Now fitted main stopcock under sink, as well as service valves on all the taps. Probably never need to do anything again, but if I do it'll be a lot easier.

Cheers

Paul